1. Field of the Invention
This invention relates generally to clinical instruments such as thermometers and more particularly to a disposable thermometer.
2. Description of the Prior Art
The cost of taking temperatures in hospitals can be divided into two parts. That is, the cost of distributing, recovering, cleaning, sterilizing, and centrifuging and the cost of replacing broken, lost and stolen thermometers. The conventional mercury-in-glass clinical thermometer has proven to be a reliable instrument despite disadvantages such as difficulty in sterilization, difficulty in reading and inherent fragility. In spite of these disadvantages the mercury-in-glass thermometer occupies a market position that has been remarkably resistant to penetration by a wide variety of electronic and chemical devices. Basically, this is because of the familiarity established over many years of daily exposure and use by millions of people. Moreover, the mercury-in-glass thermometer is convenient to use, since it can be given to a patient for temperature measurement and recovered at any time thereafter, at the convenience of the nurse, for the purpose of reading and recording the temperature indicated, whereas, direct reading electronic thermometers require the commitment of the measuring apparatus and nurse to an individual patient until the application-read-record cycle has been completed. While a mercury-in-glas thermometer is frequently inaccurate it has sufficient accuracy for all but the most unusual cases.
Recently, disposable thermometers have been developed in order to overcome the shortcomings in the mercury-in-glas thermometer. One example of a disposable thermometer is shown in U.S. Pat. No. 3,665,770 which discloses a thermally conductive sheet having a plurality of cavities each filled with a thermally responsive substance which changes from a solid to a liquid state in graduated sequence in response to the temperature of the subject being tested. U.S. Pat. No. 3,677,088 discloses another form of disposable thermometer which includes a separable shield which is removably inserted between a thermally responsive substance and an indicating means in order to prevent communication therebetween until the thermometer is acutally used so that the storage or shelf life of the thermometer will be enhanced.
The foregoing patents use devices which employ the change in state of a substance from solid to liquid (melting point) to either indicate directly U.S. Pat. No. 3,175,401 change from opaque to translucent) or indirectly (U.S. Pat. Nos. 3,704,985 and 3,677,088, etc., dissolve a dyestuff and stain a masking layer or diffuse into an indicating web).
In utilization of thermometers of this type it must be appreciated that the thermometer, either in storage or during transportation, is liable to be exposed to temperatures in excess of the intended range of application. Unless suitable means are provided, premature indication of temperature will render such a device worthless.
The devices described by Picket, Lang, et al solve the problem of premature temperature indication by separating the temperature responsive substance (material of precise melting temperature) from the indicating means (dyestuff and masking layer) until such time as it is desired to use the device, at which time the temperature responsive substance is brought into contact with the indicating means. This requires the assembly of two planar matrices (or material and indicator) with precise registration by means which are comparatively complex.
The resulting single use thermometer is a planar array of discrete assemblies of temperature responsive substance ans associated indicator means. The thermometer so formed is flexible. The temperature sensitive and indicating area is about 3/8 x 1 x 0.010 thick.
The flexibility and size make this thermometer difficult to place exactly adjacent the sublingual artery when taking oral temperatures, and make it exceedingly difficult to insert into the rectum when rectal temperature measurement is required.